2020 年 76 巻 2 号 p. I_642-I_647
The camera mounted on unmanned Aerial Vehicles (UAVs) for sea surface evaluation has recently attracted attention because it is flexible for moving and easy to use. However, it is known that the absence of measurement occurs when image quality is strongly affected by sun glitter. In this study, we develop a method to evaluate wave propagation from different oblique aerial video images. Ortho-images were created from video frames by using the collinearity equation and perspective transform. Time-averaged images were created by the average of frames during the time after that the grayscale images were calculated. The relationship between the time-averaged grayscale image and light environment was investigated by considering the reflection properties of the sea surface and the radiance distribution of incident light. This model emphasized the best observation angle. The significant wave period and the wave celerity can be evaluated from the gray-scale images. The wave spectrum, wave direction, and long-component wavelength were handled by using 2D Fourier transform and low-pass filter. As a result, applying the present method to data acquired in the Tateyama coast, the wave propagation characteristic was successfully evaluated.
